It is known to coat thin tin oxide layers on glass surfaces by exposing the heated glass to a vaporized tin compound. The tin compound may be applied as a vapor or as a fine spray which contains a dissolved tin compound.
For example, U.S. Pat. No. 3,414,429 discloses a method for applying metal oxide layers on glass containers, wherein tin(IV) halides, such as tin tetrachloride, are used as tin compounds. However, these compounds hydrolyse readily in the presence of mere traces of moisture with the formation of highly corrosive compounds. Since only a small portion of the tin halides introduced into the coating chamber is actually deposited on the glass surface and the unused portion of the tin halides cannot be recycled without considerable expenditure, the tin halides have only a limited suitability for coating or surface improving glass. Since tin tetrachloride, when used, is generally stabilized with additional hydrogen chloride, at least four chloride atoms per tin atom are obtained, which contaminate the effluent or waste water in the form of the chlorides. Moreover, because of spontaneous decomposition of tin tetrachloride, it is not unusual that a nonuniform build-up of the tin oxide layer takes place which results in optically confusing interferences.
If tin dichloride is used instead of tin tetrachloride, the amount of chloride to be disposed of is theoretically reduced. However, because of the hydrolytic instability of the aqueous solutions of tin dichloride, also in this instance hydrogen chloride has to be added to these solutions. As a result, the amount of chloride rises again above the value of 1 Sn : 2 Cl. In addition, the problem of the increased corrosion of the equipment by the hydrochloric acid-containing tin dichloride solution remains.
German Patent 25 41 710 discloses a method for applying a tin(IV) oxide layer on a glass container by the pyrolysis of a vaporized or finely divided, liquid tin compound on the surface of glass having a temperature of 450.degree. to 600.degree. C. For this method, a monoorgano tin trichloride of the general formula RSnCl.sub.3, wherein R is an alkyl radical with 1 to 8 carbon atoms, is used as tin compound. Preferably, butyl tin trichloride is used as monoalkyl tin trichloride. However, organo tin compounds are toxic products, which must be identified as such and the use of which requires special care. With respect to pollutant emission, it is a disadvantage that three chlorine atoms per tin atom are released and must be disposed of.
The glass containers provided with a tin(IV) oxide layer (hot end coated) can subsequently be additionally provided with a thin film of a natural wax or a synthetic polymer (cold end coating). Such a coating usually is transparent and makes the glass container even more resistant to scratching and abrasion, even when said container comes into contact with alkaline cleaning agents.